"The first law of politics is that almost nothing matters. Voters barely notice, much less are they moved by, the events, speeches, tactics, campaigns or even strategies that are ultimately aimed at them. Elections are largely determined by a few fundamentals: the economy, the political cycle, the basic appeal of the party leaders. The role of human agency is not trivial, but it is rarely decisive either."

In short, campaigns don't matter.

Janan Ganesh is one of our very best columnists – always thought-provoking and insightful – but on this one he's wrong. There are no settled "fundamentals" in politics – no completely objective facts – and practically everything is decided by public perceptions. The role of campaigns is critical in forming voters' opinions and good campaigns can be the difference between victory and defeat.

Campaigns ultimately matter because voters form opinions primarily based on their emotional responses to what they see and hear parties saying, not through a careful process of reasoning and rational judgement.

Hardly any voters take a detailed look at the policy documents of the parties, or even their websites, and few read serious publications like the FT. Furthermore, within reason, voters have little sense for whether things in the real world are doing a little better or a little worse. Is the economy only just growing or contracting? Is crime slightly up or down? Honestly, how many people, can really detect the difference between tiny statistical changes?

Not every voter is the same. Some form their opinions on the basis of particular politicians' views on issues that matter to them, like the environment or Europe. Others form opinions on the basis of who they trust to deliver a fair society, and others still on who they consider to be generally competent. But regardless of the final reason, the main driver in voters' choice is their emotional reaction to what senior politicians say and do in relation to what they consider to be important. It's about what voters feel.

Hearts and minds

None of this suggests that voters are in some way duped at election time, or that they are excessively naive. Rather, it reflects that voters are people - they form their opinions on political issues in much the same way they do in the rest of their life. Self-interest is important, but does not completely dictate how they behave. For example, the British people are generous in their charitable giving and are generally supportive of things like the right of refugees to come to this country – all because behaving decently and morally is important to them. Emotional appeals therefore speak to voters in ways that the public understand and sympathise with – fairness, decency, morality, competence, equality all matter.

Consider the economy. This ought to be the single biggest issue where objective truth matters and where voters take their most rational and reasoned approach. This is, after all, the issue that most affects the quality of life of voters' families. And yet there are plenty of occasions where incumbents that presided over a strengthening economy have been beaten by challenger campaigns, and plenty of occasions where parties have retained power while the economy was misfiring.

In the recent US Presidential election, Barack Obama won against the backdrop of a weak economy with very high unemployment and slow growth. He won in part because he was able to convince enough people that, while things weren't great, Mitt Romney's victory would make things harder for the "middle class". Obama's campaign persuaded many that Romney and the GOP's tax plans were for "millionaires and billionaires". They appealed to people's hearts, persuading them that improvements in the economy would never benefit them. Again, there are always two sides to every story.

The best campaigns really can deeply affect public opinion through their choices over which of their policy positions to amplify and which of their values to emphasise. But politics isn't just about public debate. Increasingly, it's about operations too and their logistical competence can also mean the difference between winning and losing. This is undoubtedly true in the US, where the Get Out The Vote operations of the parties can make a real difference in elections where the public is evenly split and where turnout matters. But it's true in Britain too. There is every reason to believe that the GOTV campaign of the Labour movement was crucial in denying the Tories a majority at the last election.

Insiders talking to insiders

Where I do sympathise with Ganesh is on his contention that much of what campaigns do passes the public by. Far too many campaigns – particularly in Britain, where we have much less of a tradition of retail politics – are excessively focused on the inside game. Too many people spend too much time scoring points on irrelevant side issues, reporting each other for obscure breaches of protocol or supposed slurs or gaffes. All these create a temporary buzz on Twitter but never hit the public radar.

But that doesn't mean the really big stuff can't or doesn't cut through to the public – if the detail doesn't, the big picture does. Good campaigns can and do articulate their general approach to issues and project an accurate depiction of their values and motives. People certainly heard Blair's change of message on tax and spend ahead of the 1997 election, and their new approach to the unions.

We should forget the idea of fundamentals of political life and focus instead on the fundamentals of public opinion – of people. People are persuadable because they are emotional. The economy will be the single biggest issue next time around but there will be two sides to the story. The Tories will argue that they are competent and their vision of fairness – one that rewards hard working people that play by the rules – is the right one. Labour will argue the Tories' economic policies have been weighted to their rich friends and their vision of competence always does. Both may be credible explanations for the state we find ourselves in – the best campaign will win out.